Control of aquatic weeds with endothall and als-inhibiting agent

ABSTRACT

Described are preferred methods and compositions for controlling aquatic weeds that involve the use of an ALS-inhibiting herbicidal agent such as penoxsulam in combination with endothall. Preferred herbicidal combinations allow for enhanced control when treating a body of water to control a target weed population, such as hydrilla.

REFERENCE TO RELATED APPLICATION

The present application claims the benefit of U.S. Provisional PatentApplication No. 61/048,147 filed Apr. 25, 2008, entitled CONTROL OFAQUATIC WEEDS WITH PENOXSULAM AND ENDOTHALL, and of U.S. ProvisionalPatent Application No. 61/148,250 filed Jan. 29, 2009, entitled CONTROLOF AQUATIC WEEDS WITH ENDOTHALL AND ALS-INHIBITING AGENT, each of whichis hereby incorporated herein by reference in its entirety.

BACKGROUND

The present invention related generally to methods and compositions forcontrolling aquatic weeds, and certain particular embodiments, methodsand compositions for selectively controlling weeds such as hydrilla orwatermilfoil utilizing a combination including penoxsulam or another ALSinhibitor herbicide and endothall.

As further background, aquatic plants very commonly arise as undesiredweeds in waters and wetlands in the United States of America andelsewhere. Two such exotic weeds are hydrilla and watermilfoil,including Eurasian watermilfoil, which present problems in ponds, lakes,and other water bodies. The treatment of such bodies of water toeliminate or control the undesired or exotic aquatic weeds is oftencomplicated by the fact that the agent used to control the undesiredweed also can detrimentally affect the health of other, desirable ornative plant life within the water body. Aquatic herbicides need to bein contact with submersed plants for a period of time (exposure time),which is dependent on the individual agent and the concentration atwhich it is used. Additionally, specific herbicides can require longexposures (months) to control certain plants in water, which can alsocause increased detriment to non-target species. Furthermore, longexposures can be difficult to maintain in a fluid environment.Insufficient exposure can lead to poor efficacy or failed treatments.Thus, methods or techniques to reduce exposure times and/or reduce theconcentrations of agents used to control submersed weeds could benefitefficacy and/or selectivity. Also, relying on a single herbicide mode ofaction can enhance the risk of selecting a resistant plant biotype tothat particular agent. Thus, treatment regimens that are more selectivefor the undesired plant species, minimize potential for resistancedevelopment, and reduce exposure times are needed.

The efficacy and application rate of herbicidal agents against thetarget aquatic weeds depends on several factors, including, the specificformulation, the plant type, climatic conditions, water and sedimentconditions in the water body, herbicide exposure time, and the like. Attimes, an inability to control an undesired plant can be eliminatedsimply by increasing the rate of application for a particular herbicidalagent. However, this is not always the case, and higher rates ofapplication can exacerbate undesired affects on beneficial plants andaquatic organisms, and may not adequately compensate for insufficientexposure with the targeted plant.

One possible way to improve aquatic weed control is to combine two ormore active compounds as part of a treatment program. However, the useof two or more active compounds often fails due to physical orbiological incompatibility, lack of stability in co-formulation,decomposition of the compounds, antagonistic effects between thecompounds, cost, and/or other factors.

In view of the background in aquatic weed control, the discovery ofenhanced or alternative methods and compositions for the control ofaquatic weeds has been a difficult endeavor. Serious needs thus remain.

SUMMARY

It has been discovered that aquatic weeds such as hydrilla can beeffectively controlled by combinations including an ALS-inhibitingherbicide, such as penoxsulam, and endothall. Aspects of the presentinvention therefore relate to methods for treating water bodies tocontrol undesired aquatic weeds with combinations including these activeagents, to compositions including such combinations, and to methods forpreparing herbicidal combination compositions which involve mixing suchactive agents to provide a combination. Still further inventiveembodiments, as well as features and advantages thereof, will beapparent from the descriptions herein.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 displays the response (biomass) of hydrilla to penoxsulam andendothall applied alone and in combination at various ratios.

FIG. 2 displays the Isobole analysis of penoxsulam and endothallmixtures on hydrilla.

FIG. 3 displays the mean hydrilla biomass from a lake in Florida treatedwith a combination of penoxsulam (0.02 ppm) and endothall (0.71 ppm) on10 Feb. 2009.

FIG. 4 displays the response (biomass) of hydrilla to imazamox andendothall applied alone and in combination at various ratios.

FIG. 5 displays the Isobole analysis of imazamox and endothall mixtureson hydrilla.

DETAILED DESCRIPTION

For the purposes of promoting an understanding of the principles of theinvention, reference will now be made to the embodiments illustrated inthe drawings and specific language will be used to describe the same. Itwill nevertheless be understood that no limitation of the scope of theinvention is thereby intended, such alterations and furthermodifications in the illustrated device, and such further applicationsof the principles of the invention as illustrated therein beingcontemplated as would normally occur to one skilled in the art to whichthe invention relates.

As discussed above, aspects of the present invention relates to methodsand compositions involving the use of penoxsulam or another ALSinhibitor herbicide in combination with endothall for controllingaquatic weeds, and especially hydrilla. Such combinations desirably:enable the use of lower levels of each herbicidal agent as compared tothat which would have to be used with each agent individually; enablethe use of sub-lethal levels of each herbicidal agent (if usedindividually); enable a reduction in the total amount of herbicideneeded for control; enable a reduction in the total exposure time neededfor control; exhibit an activity that is greater than the individualagents when used alone, more desirably a synergistic or at leastadditive effect; enhance the level of control for the target aquaticweed population; and/or enhance the selectivity for the target aquaticweed population. As well, the use of such herbicidal agent combinationsmay enhance the treatment of aquatic weed biotypes that have developedresistance to at least one of the agents included, and may benefit longterm weed control by inhibiting the development of additional resistantbiotypes.

The chemical penoxsulam(2-(2,2-difluoroethoxy)-6-trifluoromethyl-N-(5,8-dimethoxy[1,2,4]triazolo[1,5c]pyrimidin-2-yl)benzenesulfonamide))is an acetolactate synthase (ALS) or acetohydroxy acid synthase (AHAS)inhibitor. These agents inhibit the ALS or AHAS enzyme, which leads tothe depletion of key amino acids that are necessary for proteinsynthesis and plant growth (referred to as ALS-inhibiting,ALS-inhibitors, ALS compounds and the like). The following agents,although not limited to, also belong to this class: bensulfaron-methyl,bispyribac sodium, and imazamox.

The chemical endothall ((3,6-endoxohexahydrophthalic acid), also knownas (7-oxabicyclo[2.2.1]heptane-2,3-dicarboxylic acid)) is a contactherbicide. It is a membrane-active herbicide that disrupts cell functionand chemical gradients, and inhibits protein synthesis in plantmetabolism; its exact mechanism of action is unknown. Currently,endothall is commercially available for aquatic use as its dipotassiumand as its mono (N,N-dimethylalkylamine: alkyl groups as derived fromcoconut oil) salts of endothall (sold under such tradenames includingAquathol and Hydrothol).

It will be understood that herbicidal compounds such as those identifiedherein by generic name are often available as a parent compound or as anactive herbicide derivative such as a salt or ester. Accordingly, allsuch herbicidal active derivatives are intended to be encompassed by useof the generic name for the chemical, unless otherwise specified.

In accordance with certain embodiments of the invention, methods for thecontrol of hydrilla or other undesirable aquatic weeds include theapplication of a combination including penoxsulam and endothall. As toamounts, these agents will be included in a combination that iseffective to achieve control of the aquatic weed in question. Typically,for penoxsulam, such amounts will be in the range of about 1 to about 50parts per billon (ppb), or about 2.5 to about 50 ppb, more typically inthe range of about 2 to about 30 ppb or about 5 to about 40 ppb incertain embodiments; and for endothall, such amounts will be in therange of about 0.05 to about 3.5 parts per million (ppm acid equivalenceor a.e.) or about 1 to about 3.5 ppm a.e., more typically in the rangeof about 0.1 to 3.0 ppm a.e. and still more typically in the range ofabout 0.25 to 2.0 ppm a.e. It has been discovered that endothall, whenused in combination with an ALS inhibitor, can be used at low levelswhile nonetheless achieving good control of a target weed, such ashydrilla. In certain preferred embodiments of the invention, theendothall agent will thus be used in the combination at a low level,such as about 1.4 ppm a.e. or less, more preferably about 1 ppm a.e. orless, for example in certain embodiments in a range of about 0.5 to 1ppm a.e. It has also been discovered that such herbicidal combinationscan be used together without having the herbicidal agents antagonize oneanother, and in fact while achieving a surprisingly rapid control of thetarget weeds with at least an additive effect.

Methods and compositions of the invention may be used in the complete orpartial control of many noxious aquatic weeds. These include, forexample, common duckweed (Lemna minor), of the emersed plantsspatterdock (Nuphar luteum) and water-lily (Nymphaea spp.), of thesubmersed plants bladderwart (Utricularia spp.), common coontail(Ceratophyllum demersum), common elodea (Elodea canadensis), Brazilianelodea (Egeria densa) fanwort (Cabomba caroliniana), hydrilla (Hydrillaverticillata), naiad (Najas spp.), pondweed (Potamogeton spp.) includingcurlyleaf pondweed (Potamogeton crispus), watermilfoil (Myriophyllumspp.) including Eurasian watermilfoil (Myriophyllum spicatum), floatingplants including common watermeal (Woffia columbiana) and salvinia(Salvinia spp.), emersed plants including alligatorweed (Alternantheraphiloxeroides), American lotus (Nelumbo lutea), cattail (Typha spp.),creeping waterprimrose (Ludwigia peploides), parrotfeather (Myriophyllumaquaticum), smartweed (Polygonaum spp.), spikerush (Eleocharis spp.),waterpurslane (Ludwigia palustris), and watershield (Braseniaschreberi), of the submersed plants Illinois pondweed (Potamogetonillinoensis), limnophila (Limnophila sessiliflora), tapegrass orAmerican eelgrass (Vallisneria americana), and variable leafwatermilfoil (Myriophyllum heterophyllum), and the shoreline grassesbarnyardgrass (Echinochloa crusgalli), and southern watergrass(Hydrochloa caroliniensis). Particularly preferred plant types forcontrol in accordance with the invention include hydrilla, curlyleafpondweed, egeria, and watermilfoil.

For use together, it is not necessary that the penoxsulam or otherALS-inhibiting agent and endothall be applied in a physically combinedform, or even at the same time. The combination effect results so longas the two or more herbicides are present in contact with the plant atthe same time, regardless of when they were applied. Thus, for instancea physical combination of the two or more herbicides could be applied,or one or some could be applied earlier than the other(s). In certainembodiments, the herbicides will be applied within 1 to 7 days of eachother, although other embodiments may be used. Typically, theALS-inhibitor/endothall combination will be applied within about 30 daysof each other, or more typically within 1 to 21 days of each other orsimultaneously. However, the herbicides could be applied within about 30to 90 days of each other, or less, when one agent is applied in thepresence of or following an exposure to the other agent to reduceexposure time, inhibit potential for plant recovery, or enhanceefficacy. Further, it will be understood that the penoxsulam or otherALS-inhibiting herbicide and endothall can be used in combination withone or more additional herbicidal agents, for example one or moreadditional ALS inhibitor herbicidal agents and/or one or more additionalcontact type herbicidal agents, or penoxsulam could be replaced withanother ALS-inhibiting herbicide agent for aquatic use, such asbispyribac-sodium, imazamox, or bensulfuron-methyl.

In certain embodiments, a method of controlling aquatic weeds involvesthe use of a combination including bispyribac-sodium and endothall. Insuch embodiments, the endothall can be used used at a level in the rangeof about 0.1 to 3.5 ppm a.e., in certain embodiments at a level of lessthan about 1.4 ppm a.e., and typically at a level in the range of about0.35 to about 1 ppm a.e., more preferably about 0.5 to about 1 ppm a.e.;and, the bispyribac-sodium is used at a level less than about 0.5 ppm,and typically at a level in the range of about 0.01 to about 0.25 ppm,more preferably about 0.02 to about 0.1 ppm.

In other inventive embodiments, a method of controlling aquatic weedsinvolves the use of a combination including imazamox and endothall. Insuch embodiments, the endothall can be used at a level in the range ofabout 0.1 to 3.5 ppm a.e., in certain embodiments at a level of lessthan about 1.4 ppm a.e., and typically at a level in the range of about0.35 to about 1 ppm a.e., more preferably about 0.5 to about 1 ppm a.e.;and, the imazamox is used at a level less than about 0.2 ppm, andtypically at a level in the range of about 0.02 to about 0.15 ppm, morepreferably about 0.025 to about 0.075 ppm.

In further inventive embodiments, a method of controlling aquatic weedsinvolves the use of a combination including bensulfuron-methyl andendothall. In such embodiments, the endothall can be used at a level inthe range of about 0.1 to 3.5 ppm a.e., in certain embodiments at alevel of less than about 1.4 ppm a.e., and typically at a level in therange of about 0.35 to about 1 ppm a.e., more preferably about 0.5 toabout 1 ppm a.e.; and, the bensulfuron-methyl is used at a level lessthan about 0.5 ppm, and typically at a level in the range of about 0.01to about 0.25 ppm, more preferably about 0.02 to about 0.1 ppm.

Any of the herbicides can be applied separately in liquid or solid form,or a combination product containing some or all herbicides could beproduced, again, in either liquid or solid form. Typical liquidformulations include emulsions, suspensions (including suspensionscontaining microcapsules), solutions, emulsifiable concentrates, andflowables. Common solid forms include granules, wettable powders,water-dispersible solid (including water-dispersible granules containingmicroencapsulated pesticides) or dusts. The herbicidal formulation canalso contain, in addition to the active herbicide(s) other ingredientssuch as solvents, wetting agents, suspending agents, anti-caking agents,dispersing agents, emulsifiers, antifreeze agents, antifoam agents, andother additives.

Compositions according to this invention may contain the two or moreherbicides in numerous different physical forms. In some cases, acomposition may be produced by simply physically mixing (“tank mixing”)commercially available products containing the active herbicides.Alternatively, a package may be manufactured and sold which contains thetwo or more herbicides in separate containers, but packaged together,e.g. in a “multi-pack” format such as a “twin-pack” or “tri-pack”.

Alternatively, previously prepared compositions (“premixes”) containingthe two or more herbicides can be produced. Suitable liquid compositionswould include solutions or emulsions containing the two or moreherbicides. A solid product containing the two or more herbicides couldalso be produced, for instance, as impregnated granules. When premixedor tank mixed herbicidal combinations are provided, they can include thepenoxsulam or other ALS-inhibitor and endothall present in a ratio ofabout 1:2 to about 1:200 depending on the potency of the agent,respectively. In certain embodiments, premixed or tank mixed herbicidalcombinations are provided that include penoxsulam and endothall presentin a ratio of about 1:40 to about 1:700, respectively.

In use, the combination of herbicidal agents utilized should remain atherbicidal effective levels in the body of water and/or in contact withthe targeted plant for sufficient time to achieve control. In accordancewith certain preferred methods of the invention, at least one herbicidalagent level (e.g. ALS-inhibitor such as penoxsulam) will be maintainedin the body of water and/or in contact with the plant for about one tofour weeks, and in other preferred embodiments for at least about fourweeks, sometimes in the range of about four to sixteen weeks or more.The other herbicidal agent (e.g. endothall) may or may not be presentfor the duration based on chemical half-lives in water or can be addedto the other agent already in the presence of the target plant or viceversa; endothall will be present for at least about 1 day, and typicallyin the range of about 1 to 14 days or more. The concentration of anysingle herbicidal agent or both agents in the combination may bemaintained, when necessary, with the target plant to ensure efficacy,for example, through the use of sequential or bump treatments, orcontinuous injection, using the same agent.

Bodies of water to be treated with the inventive methods will typicallybe fresh water bodies such as ponds, lakes, wet lands, reservoirs,rivers or irrigation canals, although other bodies of water may also betreated in accordance with the invention.

In order to promote a farther understanding of the present invention andits various embodiments, the following specific examples are provided.It will be understood that these examples are illustrative and notlimiting of the invention.

Example 1

Control of Hydrilla with Penoxsulam and Endothall—Field Study 1

This example demonstrates that penoxsulam used in combination withendothall provides surprisingly improved hydrilla control.

A 6 acre somewhat rectangular-shaped lake was divided into three 2 acrezones for this testing. A 2-acre test site (Zone 1), located on thenorthern one-third of the lake, was treated with a penoxsulam plusendothall combination in order to evaluate control of the exotic aquaticweed, hydrilla (Hydrilla verticillata). Within a 50 gallon spray tanksystem powered by a 5.5 Hp Honda motor, 0.523 gallons Galleon SC (acommercially available penoxsulam formulation) and 12.7 gallons AquatholK (a commercially available endothall formulation) were added to 36.78gallons of water. The herbicide combination mixture delivered anapplication dose of 15 parts per billion penoxsulam and 0.71 ppm a.e.endothall to Zone 1. This herbicide mixture was evenly injected using atrailing hose over the airboat bow throughout the 2 acre Zone 1. On theday of treatment, Zone 1 contained approximately 90% hydrilla coverage,with growth near or at the water surface.

The remaining 4 acres (both Zone 2 (central one-third) and Zone 3(southern one-third)) of the lake were treated with 15 ppb penoxsulamalone on the same day. Both Zones 2 and 3 contained approximately 90-95%hydrilla coverage at that time.

Twenty one days following the initial treatment, the hydrilla wasassessed for herbicidal injury within Zones 1, 2, and 3. Unexpectedly,hydrilla plants within Zone 1, (site which received the combinationmixture treatment) were mostly necrotic, remaining stems were defoliatedand most had lost integrity. Approximately 10% of the original plantvolume remained near the water's surface; the balance had fallen to thelake bottom. The same was true for a 1 acre area contiguous down lake toZone 1 moving into Zone 2. All remaining hydrilla plants suspended inthe water column within the 3 acres were expressing severe injury.

Penoxsulam treated hydrilla typically requires about 60 days beforesevere injury is expressed and about 90 to 120 days or more beforecontrol is achieved. Endothall treatments are usually made with a 1.4 to3.5 ppm a.e. dose and typically require 2-6 weeks before hydrilla plantsdefoliate and drop toward the lake bottom, dependent on plant maturity.A 0.71 ppm a.e. endothall partial area/spot treatment applicationgenerally would provide only slight hydrilla injury, such as limiteddefoliation or apical tip necrosis, yet essentially no hydrilla control.The hydrilla damage and control level found in Zone 1 were generallysignificantly greater and more rapid than a 21 day penoxsulam treatmentat 150 ppb (maximum labeled rate) or a 3.5 ppm a.e. (maximum labeledrate) endothall treatment.

On the first evaluation date 21 days following the initial treatment,hydrilla in Zone 2 and Zone 3 expressed slight but expected penoxsulaminjury. Approximately 90% hydrilla remained near the water's surface inZone 3 and within the southern portion of Zone 2—no control was observedin these areas. On this date, 0.71 ppm a.e. endothall (12.7 gallonsAquathol K) was applied to Zone 3 in order to evaluate contactherbicidal efficacy 21 days following a penoxsulam treatment.

On the second evaluation date, sixty two days after the initialtreatments, hydrilla in Zone 1 was 100% controlled with only necroticstems present on the lake bottom. The control was present throughout the3 acre area initially impacted (Zone 1 and northern ½ of Zone 2).Hydrilla in Zone 3 was also 100% controlled. Approximately 95% hydrillacontrol was observed in the southern half of Zone 2 (1 acre) and theplants present were displaying severe injury. Therefore, the northern 1acre of Zone 2 was controlled by the original Zone 1 treatment and thesouthern portion 1 acre of Zone 2 was controlled by the intermediatetreatment that occurred twenty one days after the initial treatment. Atsixty two days, only a few severely damaged plants remained in the 6acre lake.

On a third evaluation date, one hundred and three days after the initialtreatments, no viable hydrilla could be found within the lake.Generally, at this time hydrilla would be expected to be recovering froman endothall alone treatment as being only a contact herbicide.Therefore, the combination of penoxsulam plus endothall provided fastercontrol of hydrilla than expected from endothall or penoxsulam alone,and longer-term control than expected from endothall alone. Thisherbicide combination required a lower rate of each product than wouldhave been required if each had been applied separately at normal userates.

Example 2 Penoxsulam+Endothall under Static Exposure to Hydrilla

This example demonstrates, at a minimum, an additive effect between anALS-inhibitor and endothall, and also demonstrates this effect atreduced concentrations.

Materials and Methods

Single apical meristems of hydrilla, collected from Florida, wereplanted into small pots (13.5 cm length×3.75 cm diameter) containingWallace Farm® topsoil amended with 14-14-14 slow release Osmocote®fertilizer (˜2.5 g Osmocote/kg soil) on 18 Jul. 2008. Approximately 5 to7 cm of the apical section extended above the sediment at planting, anda sand cap was placed over the potting soil (˜2 cm deep). Plants werethen transferred to a 12 L acrylic tanks filled with well water. Tankswere maintained in a growth room with 14:10 h photoperiod at 26° C.Plants were allowed to establish growth for 14 days before treatment.

Treatments were replicated three times in a completely randomizeddesign. Treatments included: untreated controls; 100, 200, 400, 800, and1600 ppb a.e. endothall; 10, 20, 40, 80, and 160 ppb penoxsulam; and200, 400, and 800 ppb of combinations of penoxsulam+endothall at ratiosof 1:39, 1:19, 1:9 and 1:4; additional concentrations of 100 ppb wereincluded with 1:9 and 1:4 ratios. Treatments were under staticconditions. Endothall was formulated as Aquathol K® (4.23 #/gallondipotassium salt; or 3#/gallon a.e.); penoxsulam was formulated asGalleon SC® (2#/gallon active ingredient). All concentrations areexpressed as a.e. for endothall.

All above ground biomass was harvested 55 days after treatment. Biomasswas dried to constant moisture at 70° C., and dry weights weredetermined. Data were subjected to regression analysis using Sigma Plotsoftware, and a GR₅₀ was determined (concentration causing a 50%reduction in dry weight). All data were analyzed forsynergism/antagonism using the Isobole analysis at the 95% confidencelevel (estimated using linear interpolation from 95% confidence bands)(Berenbaum, M. C. 1989, Pharmacological Reviews. 41:93-141; Streibig, J.C. 2003, Assessment of herbicide effects:http://www.ewrs.org/et/images/, Herbicide interaction.pdf). This modelis considered effective for determining synergism/antagonism withoutassuming that herbicides act independently when applied in combination(Green, J. M. and J. C. Streibig, 1993, Herbicide mixtures, Pages117-134 in J. C. Streibig and P. Kudsk, eds. Herbicide Bioassays. BocaRaton, Fla.: CRC). The method assumes the efficacy of herbicides incombination is equal to efficacy of the singular agents unless there issynergism or antagonism (Armel, G. R., P. L. Rardon, M. C. McComrick andN. M. Ferry, 2007, Weed Tech., 21:947-953).

Results

Data were subjected to non-linear regression to calculate GR₅₀ values(FIG. 1). The GR₅₀ for penoxsulam alone was 12 ppb and endothall alonewas 309 ppb (Table 1). The GR₅₀ for all ratios of penoxsulam andendothall combinations ranged from 57 to 295 ppb, and the valuesdecreased with increasing ratios. As the penoxsulam concentrationincreased the associated endothall concentration decreased incombination (inverse correlation). For example, the penoxsulam componentincreased from 7 to 8 to 9 to 11 ppb and the endothall componentdeclined from 288 to 149 to 84 to 46 ppb as the ratio increased from1:39, 1:19, 1:9, to 1:4, respectively.

All ratios of penoxsulam to endothall resulted in an additive effectbased on the Isobole analysis (FIG. 2). The endothall concentrationnecessary to elicit an additive response with penoxsulam was lowest inthe 1:4 ratio (57 ppb). The endothall concentration necessary to cause a50% reduction in biomass was lower in combination with penoxsulam at allratios than when applied alone under static conditions.

TABLE 1 Calculated GR₅₀ values (ppb) for penoxsulam and endothallapplied alone and at various ratios in combination to hydrilla understatic exposure. GR₅₀ Penoxsulam ppb: HERBICIDE (ppb) 95% C.I. endothallppb Penoxsulam 12  8 to 19 n/a Endothall 309 202 to 498 n/a 1:39penoxsulam:endothall 295 190 to 483 7:288 1:19 penoxsulam:endothall 157102 to 246 8:149 1:9 penoxsulam:endothall 93  62 to 141 9:84  1:4penoxsulam:endothall 57  32 to 96 11:46  Variance was estimated usinglinear interpolation from 95% confidence intervals (n = 3). The“penoxsulam ppb:endothall ppb” was calculated by multiplying the GR₅₀value times the individual ratio for each herbicide.

Positive interaction between endothall and penoxsulam was not expected.There was potential for antagonism. Endothall requires shorter exposurethan penoxsulam; endothall is a contact herbicide whereas penoxsulam isa systemic herbicide. Penoxsulam is an ALS-inhibitor that requires asustained exposure (60 to 120+days) with submersed plants to achieveeffective systemic control (SePRO Corporation, 2009, Galleon SC®Specimen Label, 11550 N. Meridian St., Suite 600, Carmel, Ind. 46032).It is active at relatively low concentrations, requiring concentrationsfrom about 0.01 to 0.15 ppm, depending on the exposure. Endothall is arelatively rapid acting contact herbicide that requires generally lessthan 72 hours of contact with hydrilla to achieve effective control(Netherland, M. D., W. R. Green and K. D. Getsinger. 1991. J. AquaticPlant Manage. 29: 61-67). Although the exact mechanism of action isunknown, it is believed to be an uncoupler of membrane transport systems(MacDonald. G. E., R. Querns, D. G. Shilling, T. A. Bewick and S. K.McDonald. 2003. J. Aquatic Plant Manage. 42: 13-18). Concentrationsgenerally range from about 1.4 to 3.5 ppm a.e. (Cerexagri Inc., 2007,Aquathol K® Specimen Label, 630 Freedom Business Center, Suite 403, Kingof Prussia, Pa. 19406). Endothall injures susceptible plants relativelyquickly with resultant loss in cell integrity, which could inhibit orpreclude effective translocation of a systemic herbicide such aspenoxsulam. However, antagonistic activity was not observed withsimultaneous treatment in this experiment, demonstrating that the agentscan be effectively used together without inhibiting the activity ofeither agent.

Example 3 Penoxsulam+Endothall under Multiple Exposures to Hydrilla

This example demonstrates that an ALS-inhibitor in combination withendothall can result in reduced exposure times, and sequencing caninfluence the interaction.

Materials and Methods

Apical sections (12 to 15 cm in length) of hydrilla, collected fromFlorida, were planted into small pots (13.5 cm length×3.75 cm diameter)containing Wallace Farm® topsoil amended with 14-14-14 slow releaseOsmocote® fertilizer (˜2.5 g Osmocote/kg soil) on 16 Oct. 2008.Approximately 5 to 7 cm of the apical section extended above thesediment at planting, and a sand cap was placed over the potting soil(˜2 cm deep). Plants were then transferred to a 12 L acrylic tanksfilled with well water. Tanks were maintained in a growth room with14:10 h photoperiod at 26° C. Plants were allowed to grow for 8 daysbefore the following treatments were initiated in triple replicate:

A) Untreated controls

B) Penoxsulam at 0.02 mg/L

C) Endothall at 0.68 mg/L a.e.

D) Simultaneous treatment

-   -   a. Penoxsulam 0.02 mg/L+endothall at 0.68 mg/L        -   i. Exposure times            -   1. 3 days            -   2. 6 days            -   3. 12 days            -   4. 24 days            -   5. 48 days (static)

E) Sequential treatment

-   -   a. Penoxsulam 0.02 mg/L, add 0.68 mg/L endothall 24 days        later—static exposure to combination    -   b. Endothall at 0.68 mg/L, add 0.02 mg/L penoxsulam 24 days        later—static exposure to combination    -   c. Penoxsulam 0.02 mg/L, add 0.68 mg/L endothall 12 days        later—12 day exposure to combination    -   d. Endothall at 0.68 mg/L, add 0.02 mg/L penoxsulam 12 days        later—12 day exposure to combination    -   e. Penoxsulam 0.02 mg/L, add 0.68 mg/L endothall 6 days later—6        day exposure to combination    -   f. Endothall at 0.68 mg/L, add 0.02 mg/L penoxsulam 6 days        later—6 day exposure to combination

Endothall was formulated as Aquathol K® (4.23 #/gallon dipotassium salt,or 3#/gallon a.e.); penoxsulam was formulated as Galleon SC® (2#/gallonactive ingredient). All concentrations are expressed as a.e. forendothall. At each exposure time, plants were removed from treatmentsand placed in a tank with fresh water containing no herbicide (includingcontrols) to remove the aqueous exposure and allow for recovery.

Plants were harvested at 48 days after initial treatment. At harvest,plants were rinsed free of algae and placed in paper sacks in a dryingoven for 4 days at 70° C. temperature. Mean dry weights were determinedand means separated using least significant differences. Differencebetween observed and expected responses was determined to evaluatepotential interactions using methods reported by Colby (Colby S. R.1967. Weeds. 15:20-22).

Results

Biomass data is presented in Table 2. Penoxsulam had greater activity onhydrilla as exposures increased, but not significantly different fromuntreated controls. This was partially expected as penoxsulam generallyrequires 60 to 120 days or longer to control submersed aquatic plants(SePRO Corporation 2009, supra). Although exposures were maintained forup to 48-days with penoxsulam, endothall likely did not remain atherbicidal levels due to its shorter half-life in water and mechanism ofbreakdown (microbial). Endothall reduced hydrilla biomass compared tountreated controls at all exposure periods, except 3 and 6-day.Treatments with combinations of endothall+penoxsulam were significantlydifferent from either herbicide alone following 12 and 24 day exposurewith a simultaneous treatment and endothall followed-by penoxsulam in12-day exposure. Combination treatments generally resulted in greatereffect than from either herbicide alone except for when penoxsulam wasfollowed-by an endothall exposure.

Simultaneous treatments of penoxsulam+endothall (3, 6, 24 and 48 dayexposures) and the sequence of penoxsulam following 6, 12, or 24 days ofan endothall treatment resulted in synergistic activity based onanalyses of interactions (Table 3). The sequencing of penoxsulamfollowed-by endothall resulted in an antagonistic effect. Thus, thecombination of penoxsulam+endothall could result in antagonism orsynergism based on sequencing. This seems counterintuitive: theeffectiveness of a contact herbicide was minimized if plants werepredisposed to a sub-lethal exposure to an ALS-inhibitor/systemicherbicide; that same ALS-inhibiting herbicide was more effective afterplants were predisposed to that same membrane disruptor/contactherbicide. As observed in example 1, penoxsulam followed-by endothallcan be an effective combination. Thus, the effectiveness of anALS-inhibitor followed-by endothall seems influenced by sequence timingmore than endothall followed-by an ALS-inhibitor.

Considering the reduced exposure times in this study compared to thoserequired with penoxsulam alone, these data indicated a synergy betweencombinations of penoxsulam plus endothall, and sequencing was important.Simultaneous application or endothall followed-by penoxsulam resulted inpositive interaction, whereas penoxsulam followed-by endothall resultedin negative interaction. The addition of endothall to penoxsulamresulted in significantly reduced exposure requirements compared topenoxsulam alone. The addition of penoxsulam to endothall resulted inpositive interaction on hydrilla regardless of the exposure timeevaluated at the concentrations tested, and at reduced endothallconcentrations.

Coupled with the results of Example 2 (static conditions) there was, ata minimum, an additive effect between an ALS-inhibitor (penoxsulam) andendothall. With various exposure times (3, 6, 12, 24, and 48 d),analyses indicated synergism between an ALS-inhibitor (penoxsulam) andendothall. Applying endothall in combination with an ALS-inhibitor, suchas penoxsulam, appeared to reduce the exposure requirement necessarywith an ALS-inhibitor to achieve systemic control, with lowerconcentrations of endothall than required when used singularly.

TABLE 2 Mean dry weight of hydrilla (n = 3) following various exposuresto combinations of endothall and penoxsulam in simultaneous combinationor in sequencing (e.g. endothall followed-by (f/b) penoxsulam). Meansfollowed by different letter are significantly different at p = 0.05according to least significant difference (LSD). TREATMENT (mg/L a.e.)3-d 6-d 12-d 24-d 48-d CONTROL 3.48ab 4.20a 3.81a 4.53a 4.63a PENOXSULAM4.01a 3.97a 3.68ab 3.24ab 2.41ab (0.02) ENDOTHALL 2.24b 2.61ab 2.72c2.14bc 1.62b (0.68) PENOXSULAM + 2.06b 1.15b 1.83d 0.11d 0.39b ENDOTHALL(0.02 + 0.68) ENDOTHALL f/b — 1.28b 0e 0.73cd — PENOXSULAM (0.68 + 0.02)PENOXSULAM f/b — 2.04b 2.87bc 1.61bcd — ENDOTHALL (0.02 + 0.68) (LSD)1.70 1.62 0.83 1.79 2.92

TABLE 3 Assessment of the interaction between endothall and penoxsulamusing methods reported by Colby (1967). DIFFERENCE EXPSOURE OBSERVEDEXPECTED IN TREATMENT (days) RESPONSE RESPONSE RESPONSE¹ PENOXSULAM(0.02) 3 115 — — ENDOTHALL (0.68) 3 64 — — PENOXSULAM + ENDOTHALL(0.02 + 0.68) 3 59 74 +15 PENOXSULAM (0.02) 6 95 — — ENDOTHALL (0.68) 662 — — PENOXSULAM + ENDOTHALL (0.02 + 0.68) 6 27 59 +32 ENDOTHALL f/bPENOXSULAM (0.68 + 0.02) 6 30 59 +29 PENOXSULAM f/b ENDOTHALL (0.02 +0.68) 6 49 59 +10 PENOXSULAM (0.02) 12 97 — — ENDOTHALL (0.68) 12 48 — —PENOXSULAM + ENDOTHALL (0.02 + 0.68) 12 48 47  −1 ENDOTHALL f/bPENOXSULAM (0.68 + 0.02) 12 0 47 +47 PENOXSULAM f/b ENDOTHALL (0.02 +0.68) 12 75 47 −28 PENOXSULAM (0.02) 24 72 — — ENDOTHALL (0.68) 24 47 —— PENOXSULAM + ENDOTHALL (0.02 + 0.68) 24 2 34 +32 ENDOTHALL f/bPENOXSULAM (0.68 + 0.02) 24 16 34 +18 PENOXSULAM f/b ENDOTHALL (0.02 +0.68) 24 36 34  −2 PENOXSULAM (0.02) 48 52 — — ENDOTHALL (0.68) 48 35 —— PENOXSULAM + ENDOTHALL (0.02 + 0.68) 48 8 18 +10 All data presented asa percent of control. ¹Calculated as difference between observed andexpected values. A positive number indicates synergism; a negativenumber indicates potential antagonism.

Example 4 Penoxsulam+Endothall Field Study 2 Materials and Methods

A 15.2 acre lake, with an average depth of 11.9 feet (Polk County, Fla.)was treated on Feb. 10, 2009 with a targeted dose of 0.02 ppm penoxsulam(Galleon SC®) and 0.71 ppm endothall (Aquathol K®). The submersed plantcommunity was dominated by hydrilla. The efficacy of the treatment onthe submersed plant community was assessed by conducting hydroacoustictransects using georeferenced echosounder data (water depth, percent ofbottom covered in vegetation (biocover) and the height of plants in thewater column). Based on these values, plant biovolume was calculated,which is a combination of biocover and height information that estimatesthe percentage of the water column occupied by submersed vegetation atany given point. Hydrilla efficacy was also assessed by collectingbiomass of hydrilla before herbicide impact and then 28 days aftertreatment. Biomass was collected from 5 to 6 random sites within aspatial area identified pretreatment with relatively uniform hydrillagrowth. Water temperature and dissolved oxygen were also measured.

Results

Hydroacoustic data indicated the biovolume of submersed plants decreasedby 85% by 28 days after treatment (Table 4). The submersed plantcommunity largely consisted of hydrilla. The hydroacoustic data wassimilar to hydrilla biomass collected which indicated an 81% decrease on10 Mar. 2009 (FIG. 3). Dissolved oxygen levels can be negativelyaffected by rapid reductions in submersed plant biomass, but dissolvedoxygen levels were maintained above critical levels following treatmentwith penoxsulam+endothall (Table 5).

Endothall is generally applied at approximately 2.1 ppm a.e. (labeledconcentrations of 1.4 to 2.8 ppm a.e.) depending on the site (Cerexagri2007, supra), and penoxsulam generally needs to be maintained for 60 to120 days or longer (SePRO Corporation 2009, supra). In combination,unexpectedly these data indicated that a reduced concentration ofendothall and a reduced exposure to penoxsulam can be effective onhydrilla.

TABLE 4 Changes in the biovolume of submersed plants (i.e. hydrilla)following treatment with the combination of penoxsulam + endothall(DAT—days after treatment). 29 Jan. 2009 24 Feb. 2009 10 Mar. 2009 DATPRETREATMENT 14 28 Biovolume 44% 12% 6.5% Percent reduction — 73%  85%

TABLE 5 Water temperature (Celsius) (TEMP) and dissolved oxygen (mg/L)(D.O.) profiles following treatment with penoxsulam + endothall in alake dominated by hydrilla (submersed plant biovolume of 44% andbiocover of 53%). 9 Feb. 2009 17 Feb. 2009 24 Feb. 2009 27 Feb. 2009 3Mar. 2009 10 Mar. 2009 14:00 hours 11:50 hours 13:15 hours 07:00 hours09:00 hours 10:15 hours FEET TEMP DO TEMP DO TEMP DO TEMP DO TEMP DOTEMP DO 1 16.6 8.5 18.9 6.9 18.8 6.5 18.7 6.8 17.7 5.7 21.7 6.6 2 16.68.5 18.9 6.5 18.7 6.5 18.6 6.6 17.7 5.7 21.5 6.7 3 16.5 8.0 18.9 6.918.6 6.2 18.6 6.5 17.7 5.5 21.4 6.0 4 16.4 8.0 18.8 6.9 18.4 6.2 18.66.5 17.7 5.6 21.2 6.3 5 15.2 7.3 18.8 6.9 18.2 6.0 18.6 6.5 17.7 5.620.5 5.1 6 15.1 7.3 18.5 6.5 18.1 6.0 18.6 6.5 17.7 5.6 19.9 5.8 7 15.17.3 18.2 6.2 18.0 5.7 18.6 6.3 17.7 5.6 19.3 6.7 8 15.0 7.3 16.9 6.517.9 5.8 18.6 6.3 17.7 5.6 18.8 6.5 9 14.9 7.3 16.5 6.6 17.8 6.3 18.35.4 17.7 5.6 18.6 5.8 10 — — 16.5 6.6 17.7 6.0 18.2 5.2 17.7 5.6 18.45.5 11 — — 16.5 6.6 17.7 6.0 18.0 5.0 17.7 5.6 18.2 4.4 12 — — 15.7 5.517.6 5.0 17.7 4.0 17.7 5.6 18.1 3.7 13 — — — — 16.7 3.1 17.4 3.0 17.75.6 18.0 3.4 14 — — — — 16.5 3.0 17.3 3.0 — — — —

Example 5 Imazamox+Endothall under Static Exposure to Hydrilla

This example demonstrates that the ratio of an ALS-inhibitor incombination with endothall can influence interaction.

Materials and Methods

Single apical meristems of hydrilla, collected from Florida, wereplanted into small pots (13.5 cm length×3.75 cm diameter) containingWallace Farm® topsoil amended with 14-14-14 slow release Osmocote®fertilizer (˜2.5 g Osmocote/kg soil) on 4 Nov. 2008. Approximately 5 to7 cm of the apical section extended above the sediment at planting, anda sand cap was placed over the potting soil (˜2 cm deep). Plants werethen transferred to a 12 L acrylic tanks filled with well water. Tankswere maintained in a growth room with 14:10 h photoperiod at 26° C.Plants were allowed to establish growth for 10 days before treatment.

Treatments were replicated three times in a completely randomizeddesign. Treatments included: untreated controls; 100, 200, 400, 600, and800 ppb a.e. endothall; 25, 50, 100, 200, and 400 ppb imazamox; and 200,400, 600 and 800 ppb of combinations of endothall plus imazamox atratios of 19:1, 9:1, and 5.7:1. Treatments were under static conditions.Endothall was formulated as Aquathol K® (4.23 #/gallon dipotassium salt,or 3#/gallon a.e.); imazamox was formulated as Raptor® (1#/gallon activeingredient). All concentrations are expressed as a.e. for endothall.

All above ground biomass was harvested 34 days after treatment. Biomasswas dried to constant moisture at 70° C., and dry weights weredetermined. Data were subjected to regression analysis using Sigma Plotsoftware, and a GR₅₀ was determined (concentration causing a 50%reduction in dry weight). All data were analyzed forsynergism/antagonism using the Isobole analysis at the 95% confidencelevel (estimated using linear interpolation from 95% confidence bands)(refer to Example 2 for more information on Isobole analysis).

Results

Data were subjected to non-linear regression to calculate GR₅₀ values(FIG. 4). The GR₅₀ for imazamox alone was 680 ppb and endothall alonewas 520 ppb (Table 6). The GR₅₀ for all ratios of penoxsulam andendothall combinations ranged from 455 to 784 ppb. Depending on theratio of endothall to imazamox, various interactions occurred rangingfrom antagonism to synergism based on the Isobole analysis (FIG. 5). Aratio of 19:1 resulted in an additive effect, 9:1 resulted in synergy,and 5.7:1 resulted in antagonism. Thus, the ratio of endothall:imazamoxwas critical to enhancing efficacy when applied in combination to reduceexposure requirements or reduce concentrations of at least one of theagents in the mixture.

TABLE 6 Calculated GR₅₀ values (ppb) for imazamox and endothall appliedalone and at various ratios in combination to hydrilla under static.GR₅₀ Endothall ppb: HERBICIDE (ppb) 95% C.I. imazamox ppb Imazamox 680355 to 1751 n/a Endothall 520 467 to 679 n/a 19:1 endothall:imazamox 551503 to 641 523:28 9:1 endothall:imazamox 455 426 to 484 410:46 5.7:1endothall:imazamox 784 651 to 1118 666:118 Variance was estimated usinglinear interpolation from 95% confidence intervals (n = 3). The“endothall ppb:imazamox ppb” was calculated by multiplying the GR₅₀value times the individual ratio for each herbicide.

The uses of the terms “a” and “an” and “the” and similar references inthe context of describing the invention (especially in the context ofthe following claims) are to be construed to cover both the singular andthe plural, unless otherwise indicated herein or clearly contradicted bycontext. Recitation of ranges of values herein are merely intended toserve as a shorthand method of referring individually to each separatevalue falling within the range, unless otherwise indicated herein, andeach separate value is incorporated into the specification as if it wereindividually recited herein. All methods described herein can beperformed in any suitable order unless otherwise indicated herein orotherwise clearly contradicted by context. The use of any and allexamples, or exemplary language (e.g., “such as”) provided herein, isintended merely to better illuminate the invention and does not pose alimitation on the scope of the invention unless otherwise claimed. Nolanguage in the specification should be construed as indicating anynon-claimed element as essential to the practice of the invention.

While the invention has been illustrated and described in detail in thedrawings and foregoing description, the same is to be considered asillustrative and not restrictive in character, it being understood thatonly the preferred embodiment has been shown and described and that allchanges and modifications that come within the spirit of the inventionare desired to be protected. In addition, all references cited hereinare indicative of the level of skill in the art and are herebyincorporated by reference in their entirety.

1. A method for controlling aquatic weeds in a body of water,comprising: providing in the body of water an herbicidal combinationincluding penoxsulam and endothall, so as to control the aquatic weeds.2. The method of claim 1, wherein the aquatic weeds include hydrilla. 3.The method of claim 1, wherein said providing comprises applying theendothall and penoxsulam to the body of water within 24 hours of oneanother.
 4. The method of claim 1, wherein said providing comprisesapplying the endothall and penoxsulam at least 24 hours apart from oneanother.
 6. The method of claim 1, wherein the penoxsulam is applied tothe body of water at a level of about 2.5 to 50 ppb.
 7. The method ofclaim 1, wherein the endothall is applied to the body of water at alevel of about 0.1 to 3.5 ppm a.e.
 8. An herbicidal composition,comprising: an herbicidal combination including penoxsulam andendothall.
 9. The herbicidal composition of claim 8, wherein thepenoxsulam and endothall are present in a ratio of about 1:2 to about1:200, respectively.
 10. A multi-pack herbicide product, comprising: afirst container containing an ALS-inhibiting herbicide; a secondcontainer containing endothall; and a package holding said firstcontainer and second container.
 11. The product of claim 10, wherein theALS-inhibiting herbicide is penoxsulam.
 12. The product of claim 10,wherein the ALS-inhibiting herbicide is imazamox.
 13. The product ofclaim 10, wherein the ALS-inhibiting herbicide is bensulfuron-methyl.14. A method for controlling aquatic weeds in a body of water,comprising: providing in the body of water an herbicidal combinationincluding an ALS-inhibiting herbicide and endothall, so as to controlthe aquatic weeds.
 15. The method of claim 14, wherein said providingcomprises providing the endothall at a level of about 1.4 ppm or less inthe body of water.
 16. The method of claim 15, wherein theALS-inhibiting herbicide is penoxsulam.
 17. The method of claim 15,wherein the ALS-inhibiting herbicide is imazamox.
 18. The method ofclaim 15, wherein the ALS-inhibiting herbicide is bensulfaron-methyl.19. The method of claim 15, wherein the ALS-inhibiting herbicide isbispyribac sodium.
 20. The method of claim 14, wherein aquatic weedsinclude hydrilla.
 21. The method of claim 14, wherein said providingcomprises providing the endothall at a level of about 0.1 to about 3.5ppm in the body of water.